Since the discovery of the phenomenon of swelling in invertebrate nerve fiber in 1980, our effort has been directed toward the following two goals: (1) to improve our mechanoelectric transducers and expand our investigation to include other excitable cells and tissues, and (2) to clarify the nature of the phenomenon of swelling on a physicochemical basis. Last year, we found that the frog dorsal root ganglion swells when invaded by an afferent volley of impulses. We found also that there is a large mechanical movement in the frog spinal cord following stimulation of the dorsal roots. During the year just past, we found complex movements of the isolated retinas of the squid, crab, lobster and bullfrog. Since invertebrate eyes contain a limited number of photosensitive cells, our analyses of the newly discovered phenomenon was straightforward. We came to the conclusion that the movement of water molecules associated with release and uptake of Ca-ions play a crucial role in photoelectric transduction. A study of mechanical movements of the bullfrog retina is in progress. Quite recently, we found rapid mechanical movements of the bullfrog sympathetic ganglion produced by ortho- and anti-dromic volley of impulses. In addition to the swelling associated with action potential production in the preganglionic fibers and in the ganglion cells, we could record, from deeply curarized ganglia, mechanical changes associated with the excitatory postsynaptic potential. We believe that studies of these mechanical changes in synapses yield important information as to the mechanism of synaptic transmission.